Oleander (Nerium oleander) is a hardy, easy-to-grow flowering plant, mainly found in the lower half of the US.Apart from making an appearance in gardens from coast to coast, in many states â including California â â¦ Unfortunately, the Oleander plant is toxic for all â¦ Unfortunately, oleander in the landscape is considered to be highly toxic whether the plant is fresh or dried. Poisonous Plants for Dogs and Cats: Oleander. Is oleander poisonous? The plant contains chemicals (cardiac glycosides: nerioside, oleandroside; saponins) which are very toxic if ingested. Oleander poisoning: The oleander is a flowering shrub or small tree which bears clusters of flowers. Oleanders are beautiful flowering plants that can grow incredibly large. Nerium oleander is a popular ornamental garden plant due to its beauty and tolerance of poor soil and drought, but unfortunately itâs very toxic to many species of animals. Dogs, cats, goats, cattle, sheep, camelids, budgerigaries, rabbits and horses are all species that have been affected by oleander. Rule number one: Always listen to your mama. Oleanders are commonly used in landscaping along fences for privacy and for their beauty. The good news is that there have been very few reports of human death due to oleander toxicity, probably due to the plantâs vile taste, says University of Wisconsinâs BioWeb. Oleander poisoning: Introduction. Nerium oleander is a highly toxic plant from the Apocynaceae family. Oleander Toxicity. The plant originated from Eurasia and is often used as an ornamental plant.